Hexamethyldisilazane

Structural formula
General
Surname	1,1,1,3,3,3-hexamethyldisilazane
other names	Hexamethyldisilazane HMDS Bis (trimethylsilyl) amine
Molecular formula	C 6 H 19 NSi 2
Brief description	colorless liquid
External identifiers / databases
CAS number 999-97-3 EC number 213-668-5 ECHA InfoCard 100.012.425 PubChem 13838 Wikidata Q425001
properties
Molar mass	161.39 g mol −1
Physical state	liquid
density	0.78 g cm −3 (20 ° C)
Melting point	−82 ° C
boiling point	127 ° C
Vapor pressure	20 h Pa (20 ° C)
solubility	decomposes in water
Refractive index	1.4069-1.4089
safety instructions
GHS labeling of hazardous substances danger H and P phrases H: 225-302-311 + 331-314 P: 210-280-301 + 330 + 331-302 + 352-304 + 340-305 + 351 + 338-308 + 310-403 + 235
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions . Refractive index: Na-D line , 20 ° C

Hexamethyldisilazane , short HMDS , molecular formula C ₆ H ₁₉ NSi ₂ , is widely used for the surface modification of solid surfaces, such. As for waterproofing of silica particles or to improve the adhesion of photoresists for semiconductor surfaces . In the semiconductor industry, the chemical vapor deposition (CVD) method allows HMDS to be applied easily.

In organic chemistry , hexamethyldisilazane is used, among other things, to introduce trimethylsilyl groups . In comparison to chlorotrimethylsilane , the handling is more comfortable, since hexamethyldisilazane is quite insensitive to water and humidity. In addition, there is no need to add an auxiliary base , since only ammonia occurs as a by-product in the silylation . For this, a higher reaction temperature usually has to be used, which can be a disadvantage with sensitive substrates.

Extraction and presentation

Hexamethyldisilazane can be obtained by reacting trimethylsilyl chloride with ammonia .

${\displaystyle \mathrm {2\ (CH_{3})_{3}SiCl+3\ NH_{3}\longrightarrow [(CH_{3})_{3}Si]_{2}NH+2\ NH_{4}Cl} }$

properties

Hexamethyldisilazane is a colorless to yellow colored liquid with an amine- like odor that is highly flammable. The compound has a flash point below 15 ° C. The explosion range is between 0.8% by volume as the lower explosion limit (LEL) and 25.9% by volume as the upper explosion limit (UEL). The ignition temperature is 325 ° C. The substance therefore falls into temperature class T2. Moisture causes slow hydrolysis with the formation of hexamethyldisiloxane and ammonia . Upon contact with water, the compound is first hydrolyzed in a violent reaction with evolution of heat and formation of ammonia to trimethylsilanol, which is unstable and condenses with elimination of water to form water-insoluble hexamethyldisiloxane (bis (trimethylsilyl) ether). The heat of hydrolysis is −144.4 kJ mol ⁻¹ .

Hazard assessment

In 2014, hexamethyldisilazane was included in the EU's ongoing action plan ( CoRAP ) in accordance with Regulation (EC) No. 1907/2006 (REACH) as part of substance evaluation . The effects of the substance on human health and the environment are re-evaluated and, if necessary, follow-up measures are initiated. The causes for the uptake of hexamethyldisilazane were concerns about high (aggregated) tonnage and high risk characterization ratio (RCR). The re-evaluation took place from 2014 and was carried out by Spain . A final report was then published, but no changes were recommended.

Individual evidence

1. ↑ ^{a b c d e f g h i j} Entry on 1,1,1,3,3,3-hexamethyldisilazane in the GESTIS substance database of the IFA , accessed on January 10, 2017(JavaScript required) .
2. ↑ Entry on hexamethyldisilazane at ChemBlink , accessed on February 25, 2011.
3. ↑ Phillip Laube: HMDS. In: Lexicon - Semiconductor Technology from A to Z. Accessed April 19, 2011 . 
4. ↑ Georg Brauer (Ed.), With the collaboration of Marianne Baudler a . a .: Handbook of Preparative Inorganic Chemistry. 3rd, revised edition. Volume I, Ferdinand Enke, Stuttgart 1975, ISBN 3-432-02328-6 , p. 711.
5. ↑ Entry on 1,1,1,3,3,3-hexamethyldisilazane. In: Römpp Online . Georg Thieme Verlag, accessed on June 14, 2014.
6. ↑ AEBeezer, CT Mortimer: Heat of formation and bond energies. Part XV. Chlorotrimethylsilane and Hexamethyldisilazane. In: J. Chem. Soc. A, 1966, pp. 514-516, doi : 10.1039 / J19660000514 .
7. ^ European Chemicals Agency (ECHA): Substance Evaluation Report and Conclusion Document .
8. ↑ Community rolling action plan ( CoRAP ) of the European Chemicals Agency (ECHA): 1,1,1,3,3,3-hexamethyldisilazane , accessed on March 26, 2019.